Substrate pretreatment and etch uniformity in nanoimprint lithography

ABSTRACT

A nanoimprint lithography method includes contacting a composite polymerizable coating formed from a pretreatment composition and an imprint resist with a nanoimprint lithography template defining recesses. The composite polymerizable coating is polymerized to yield a composite polymeric layer defining a pre-etch plurality of protrusions corresponding to the recesses of the nanoimprint lithography template. The nanoimprint lithography template is separated from the composite polymeric layer. At least one of the pre-etch plurality of protrusions corresponds to a boundary between two of the discrete portions of the imprint resist, and the pre-etch plurality of protrusions have a variation in pre-etch height of ±10% of a pre-etch average height. The pre-etch plurality of protrusions is etched to yield a post-etch plurality of protrusions having a variation in post-etch height of ±10% of a post-etch average height, and the pre-etch average height exceeds the post-etch average height.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application Ser. No. 62/355,814 entitled “SUBSTRATE PRETREATMENT AND ETCH UNIFORMITY IN NANOIMPRINT LITHOGRAPHY” filed on Jun. 28, 2016, and is a continuation-in-part of U.S. application Ser. No. 15/195,789 entitled “SUBSTRATE PRETREATMENT FOR REDUCING FILL TIME IN NANOIMPRINT LITHOGRAPHY” filed on Jun. 28, 2016, which is a continuation-in-part of U.S. application Ser. No. 15/004,679 entitled “SUBSTRATE PRETREATMENT FOR REDUCING FILL TIME IN NANOIMPRINT LITHOGRAPHY” filed on Jan. 22, 2016, which claims priority to U.S. Application Ser. No. 62/215,316 entitled “SUBSTRATE PRETREATMENT FOR REDUCING FILL TIME IN NANOIMPRINT LITHOGRAPHY” filed on Sep. 8, 2015, all of which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

This invention relates to facilitating throughput in nanoimprint lithography processes by treating a nanoimprint lithography substrate with a pretreatment composition to promote spreading of an imprint resist on the nanoimprint lithography substrate, and matching the etch rate of the pretreatment composition and the imprint resist to achieve uniform etching across the imprinted field.

BACKGROUND

As the semiconductor processing industry strives for larger production yields while increasing the number of circuits per unit area, attention has been focused on the continued development of reliable high-resolution patterning techniques. One such technique in use today is commonly referred to as imprint lithography. Imprint lithography processes are described in detail in numerous publications, such as U.S. Patent Application Publication No. 2004/0065252, and U.S. Pat. Nos. 6,936,194 and 8,349,241, all of which are incorporated by reference herein. Other areas of development in which imprint lithography has been employed include biotechnology, optical technology, and mechanical systems.

An imprint lithography technique disclosed in each of the aforementioned patent documents includes formation of a relief pattern in an imprint resist and transferring a pattern corresponding to the relief pattern into an underlying substrate. The patterning process uses a template spaced apart from the substrate and a polymerizable composition (an “imprint resist”) disposed between the template and the substrate. In some cases, the imprint resist is disposed on the substrate in the form of discrete, spaced-apart drops. The drops are allowed to spread before the imprint resist is contacted with the template. After the imprint resist is contacted with the template, the resist is allowed to uniformly fill the space between the substrate and the template, then the imprint resist is solidified to form a layer that has a pattern conforming to a shape of the surface of the template. After solidification, the template is separated from the patterned layer such that the template and the substrate are spaced apart.

Throughput in an imprint lithography process generally depends on a variety of factors. When the imprint resist is disposed on the substrate in the form of discrete, spaced-apart drops, throughput depends at least in part on the efficiency and uniformity of spreading of the drops on the substrate. Spreading of the imprint resist may be inhibited by factors such as gas voids between the drops and incomplete wetting of the substrate and/or the template by the drops. Spreading of the imprint resist may be facilitated by pretreating the substrate with a composition having a higher surface tension than that of the imprint resist. However, the difference in composition of the pretreatment composition and the imprint resist, together with a non-uniform distribution of the pretreatment composition and the imprint resist may cause non-uniform etching across the field, resulting in poor critical dimension uniformity or incomplete etching.

SUMMARY

In a first general aspect, a nanoimprint lithography method includes disposing a pretreatment composition on a nanoimprint lithography substrate to yield a liquid pretreatment coating on the nanoimprint lithography substrate, disposing discrete portions of an imprint resist on the pretreatment coating, and forming a composite polymerizable coating on the nanoimprint lithography substrate as each discrete portion of the imprint resist spreads on the liquid pretreatment coating. The pretreatment composition includes a polymerizable component, and the imprint resist is a polymerizable composition. The composite polymerizable coating is contacted with a nanoimprint lithography template defining recesses, and the composite polymerizable coating is polymerized to yield a composite polymeric layer defining a pre-etch plurality of protrusions corresponding to the recesses of the nanoimprint lithography template. At least one of the pre-etch plurality of protrusions corresponds to a boundary between two of the discrete portions of the imprint resist, and the pre-etch plurality of protrusions has a variation in pre-etch height of ±10% of a pre-etch average height. The nanoimprint lithography template is separated from the composite polymeric layer, and the pre-etch plurality of protrusions is etched to yield a post-etch plurality of protrusions. The post-etch plurality of protrusions has a variation in post-etch height of ±10% of a post-etch average height, and the pre-etch average height exceeds the post-etch average height.

Implementations of the first general aspect may include one or more of the following features.

The pre-etch average height may be up to 1 μm, up to 500 nm, or up to 200 nm. The variation in post-etch height may be ±5% or ±2% of the post-etch average height. At least two of the pre-etch plurality of protrusions correspond to boundaries between two of the discrete portions of the imprint resist. In some cases, each protrusion in the pre-etch plurality of protrusions has a width in a range of 5 nm to 100 μm along a dimension of the nanoimprint lithography substrate. In certain cases, the pre-etch plurality of protrusions corresponds to a linear dimension of up to 50 mm along a dimension of the nanoimprint lithography substrate. The boundary between the two of the discrete portions of the imprint resist may be formed from an inhomogeneous mixture of the imprint resist and the pretreatment composition. The pre-etch average height typically exceeds the post-etch average height by at least 1 nm. The pre-etch height and the post-etch height are assessed at intervals in a range of 1 μm to 50 μm along a dimension of the nanoimprint lithography substrate.

Etching the pre-etch plurality of protrusions may include exposing the plurality of protrusions to an oxygen- or halogen-containing plasma. The pre-etch height and the post-etch height may be assessed by atomic force microscopy, reflectometry, ellipsometry, or profilometry.

In some cases, the interfacial surface energy between the pretreatment composition and air exceeds the interfacial surface energy between the imprint resist and air or between at least a component of the imprint resist and air. The difference between the interfacial surface energy between the pretreatment composition and air and the interfacial surface energy between the imprint resist and air may be in a range of 0.5 mN/m to 25 mN/m, 0.5 mN/m to 15 mN/m, or 0.5 mN/m to 7 mN/m; the interfacial surface energy between the imprint resist and air may be in a range of 20 mN/m to 60 mN/m, 28 mN/m to 40 mN/m, or 32 mN/m to 35 mN/m; and the interfacial surface energy between the pretreatment composition and air may be in a range of 30 mN/m to 45 mN/m. The viscosity of the pretreatment composition may be in a range of 1 cP to 200 cP, 1 cP to 100 cP, or 1 cP to 50 cP at 23° C. The viscosity of the imprint resist may be in a range of 1 cP to 50 cP, 1 cP to 25 cP, or 5 cP to 15 cP at 23° C.

The pretreatment composition may include or consist essentially of a single monomer. In some cases, the pretreatment composition is a single monomer. In some cases, the pretreatment composition includes two or more monomers. The pretreatment composition may include a monofunctional, difunctional, or multifunctional acrylate monomer. In certain cases, the pretreatment composition includes at least one of tricyclodecanedimethanol diacrylate, 1,3-adamantanediol diacrylate, m-xylylene diacrylate, p-xylylene diacrylate, 2-phenyl-1,3-propanediol diacrylate, phenylethyleneglycol diacrylate, 1,9-nonanediol diacrylate, 1,12-dodecanediol diacrylate, and trimethylolpropane triacrylate. The imprint resist may include at least one of benzyl acrylate, m-xylylene diacrylate, p-xylylene diacrylate, 2-phenyl-1,3-propanediol diacrylate, and phenylethyleneglycol diacrylate.

The imprint resist may include 0 wt % to 80 wt %, 20 wt % to 80 wt %, or 40 wt % to 80 wt % of one or more monofunctional acrylates; 20 wt % to 98 wt % of one or more difunctional or multifunctional acrylates; 1 wt % to 10 wt % of one or more photoinitiators; and 1 wt % to 10 wt % of one or more surfactants. The imprint resist may include 90 wt % to 98 wt % of one or more difunctional or multifunctional acrylates and may be essentially free of monofunctional acrylates. The imprint resist may include one or more monofunctional acrylates and 20 wt % to 75 wt % of one or more difunctional or multifunctional acrylates.

In some cases, the polymerizable component of the pretreatment composition and a polymerizable component of the imprint resist react to form a covalent bond during the polymerizing of the composite polymerizable coating.

Disposing the pretreatment composition on the nanoimprint lithography substrate may include spin coating the pretreatment composition on the nanoimprint lithography substrate. Disposing discrete portions of the imprint resist on the pretreatment coating may include dispensing drops of the imprint resist on the pretreatment coating.

A second general aspect includes a nanoimprint lithography stack formed by the first general aspect.

A third general aspect includes a method for manufacturing a device, the method including the nanoimprint lithography method of the first general aspect.

A fourth general aspect includes the device formed by the method of the third general aspect.

In a fifth general aspect, a nanoimprint lithography stack includes a nanoimprint lithography substrate and a composite polymeric layer on the nanoimprint lithography substrate. The composite polymeric layer is formed from discrete portions of an imprint resist on a pretreatment coating and defines a pre-etch plurality of protrusions. At least one of the protrusions corresponds to a boundary between two of the discrete portions of the imprint resist, and the pre-etch plurality of protrusions has a variation in pre-etch height of ±10% of a pre-etch average height. After etching of the pre-etch plurality of protrusions to yield a post-etch plurality of protrusions, the post-etch plurality of protrusions has a variation in post-etch height of ±10% of a post-etch average height, and the pre-etch average height exceeds the post-etch average height.

Implementations of the fifth general aspect may include one or more of the following features.

In some cases, the boundary between the two of the discrete portions of the imprint resist is formed from an inhomogeneous mixture of the pretreatment composition and the imprint resist. In certain cases, the variation in post-etch average height is ±5% of the post-etch average height.

The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified side view of a lithographic system.

FIG. 2 depicts a simplified side view of the substrate shown in FIG. 1, with a patterned layer formed on the substrate.

FIGS. 3A-3D depict spreading interactions between a drop of a second liquid on a layer of a first liquid.

FIG. 4 is a flowchart depicting a process for facilitating nanoimprint lithography throughput.

FIG. 5A depicts a nanoimprint lithography substrate. FIG. 5B depicts a pretreatment coating disposed on a nanoimprint lithography substrate.

FIGS. 6A-6D depict formation of a composite coating from drops of imprint resist disposed on a substrate having a pretreatment coating.

FIGS. 7A-7D depict cross-sectional views along lines w-w, x-x, y-y, and z-z of FIGS. 6A-6D, respectively.

FIGS. 8A and 8B depict cross-sectional views of a pretreatment coating displaced by drops on a nanoimprint lithography substrate.

FIGS. 9A-9C depict cross-sectional views of a template in contact with a homogeneous composite coating and the resulting nanoimprint lithography stack.

FIGS. 10A-10C depict cross-sectional views of a template in contact with an inhomogeneous composite coating and the resulting nanoimprint lithography stack.

FIG. 11 is an image of drops of an imprint resist after spreading on an adhesion layer of a substrate without a pretreatment coating, corresponding to Comparative Example 1.

FIG. 12 is an image of drops of an imprint resist after spreading on a pretreatment coating as described in Example 1.

FIG. 13 is an image of drops of an imprint resist after spreading on a pretreatment coating as described in Example 2.

FIG. 14 is an image of drops of an imprint resist after spreading on a pretreatment coating as described in Example 3.

FIG. 15 shows defect density as a function of prespreading time for the imprint resist and pretreatment of Example 2.

FIG. 16 shows drop diameter versus time for spreading pretreatment compositions.

FIG. 17A shows viscosity as a function of fractional composition of one component in a two-component pretreatment composition. FIG. 17B shows drop diameter versus time for various ratios of components in a two-component pretreatment composition. FIG. 17C shows surface tension of a two-component pretreatment composition versus fraction of one component in the two-component pretreatment composition.

FIG. 18 shows etch rates of pretreatment compositions relative to the etch rate of an imprint resist.

FIGS. 19A and 19B show imprint feature height of imprint patterns before and after etching.

DETAILED DESCRIPTION

FIG. 1 depicts an imprint lithographic system 100 of the sort used to form a relief pattern on substrate 102. Substrate 102 may include a base and an adhesion layer adhered to the base. Substrate 102 may be coupled to substrate chuck 104. As illustrated, substrate chuck 104 is a vacuum chuck. Substrate chuck 104, however, may be any chuck including, but not limited to, vacuum, pin-type, groove-type, electromagnetic, and/or the like. Exemplary chucks are described in U.S. Pat. No. 6,873,087, which is incorporated by reference herein. Substrate 102 and substrate chuck 104 may be further supported by stage 106. Stage 106 may provide motion about the x-, y-, and z-axes. Stage 106, substrate 102, and substrate chuck 104 may also be positioned on a base.

Spaced apart from substrate 102 is a template 108. Template 108 generally includes a rectangular or square mesa 110 some distance from the surface of the template towards substrate 102. A surface of mesa 110 may be patterned. In some cases, mesa 110 is referred to as mold 110 or mask 110. Template 108, mold 110, or both may be formed from such materials including, but not limited to, fused silica, quartz, silicon, silicon nitride, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal (e.g., chrome, tantalum), hardened sapphire, or the like, or a combination thereof. As illustrated, patterning of surface 112 includes features defined by a plurality of spaced-apart recesses 114 and protrusions 116, though embodiments are not limited to such configurations. Patterning of surface 112 may define any original pattern that forms the basis of a pattern to be formed on substrate 102.

Template 108 is coupled to chuck 118. Chuck 118 is typically configured as, but not limited to, vacuum, pin-type, groove-type, electromagnetic, or other similar chuck types. Exemplary chucks are further described in U.S. Pat. No. 6,873,087, which is incorporated by reference herein. Further, chuck 118 may be coupled to imprint head 120 such that chuck 118 and/or imprint head 120 may be configured to facilitate movement of template 108.

System 100 may further include a fluid dispense system 122. Fluid dispense system 122 may be used to deposit imprint resist 124 on substrate 102. Imprint resist 124 may be dispensed upon substrate 102 using techniques such as drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, or the like. In a drop dispense method, imprint resist 124 is disposed on substrate 102 in the form of discrete, spaced-apart drops, as depicted in FIG. 1.

System 100 may further include an energy source 126 coupled to direct energy along path 128. Imprint head 120 and stage 106 may be configured to position template 108 and substrate 102 in superimposition with path 128. System 100 may be regulated by a processor 130 in communication with stage 106, imprint head 120, fluid dispense system 122, and/or source 126, and may operate on a computer readable program stored in memory 132.

Imprint head 120 may apply a force to template 108 such that mold 110 contacts imprint resist 124. After the desired volume is filled with imprint resist 124, source 126 produces energy (e.g., electromagnetic radiation or thermal energy), causing imprint resist 124 to solidify (e.g., polymerize and/or crosslink), conforming to the shape of surface 134 of substrate 102 and patterning surface 112. After solidification of imprint resist 124 to yield a polymeric layer on substrate 102, mold 110 is separated from the polymeric layer.

FIG. 2 depicts nanoimprint lithography stack 200 formed by solidifying imprint resist 124 to yield patterned polymeric layer 202 on substrate 102. Patterned layer 202 may include a residual layer 204 and a plurality of features shown as protrusions 206 and recesses 208, with protrusions 206 having a thickness t₁ and residual layer 204 having a thickness t2. In nanoimprint lithography, a length of one or more protrusions 206, recessions 208, or both parallel to substrate 102 is less than 100 nm, less than 50 nm, or less than 25 nm. In some cases, a length of one or more protrusions 206, recessions 208, or both is between 1 nm and 25 nm or between 1 nm and 10 nm.

The above-described system and process may be further implemented in imprint lithography processes and systems such as those referred to in U.S. Pat. Nos. 6,932,934; 7,077,992; 7,197,396; and 7,396,475, all of which are incorporated by reference herein.

For a drop-on-demand or drop dispense nanoimprint lithography process, in which imprint resist 124 is disposed on substrate 102 as discrete portions (“drops”), as depicted in FIG. 1, the drops of the imprint resist typically spread on the substrate 102 before and after mold 110 contacts the imprint resist. If the spreading of the drops of imprint resist 124 is insufficient to cover substrate 102 or fill recesses 114 of mold 110, polymeric layer 202 may be formed with defects in the form of voids. Thus, a drop-on-demand nanoimprint lithography process typically includes a delay between initiation of dispensation of the drops of imprint resist 124 and initiation of movement of the mold 110 toward the imprint resist on the substrate 102 and subsequent filling of the space between the substrate and the template. Thus, throughput of an automated nanoimprint lithography process is generally limited by the rate of spreading of the imprint resist on the substrate and filling of the template. Accordingly, throughput of a drop-on-demand or drop dispense nanoimprint lithography process may be improved by reducing “fill time” (i.e., the time required to completely fill the space between the template and substrate without voids). One way to decrease fill time is to increase the rate of spreading of the drops of the imprint resist and coverage of the substrate with the imprint resist before movement of the mold toward the substrate is initiated. The rate of spreading of an imprint resist and the uniformity of coverage of the substrate may be improved by pretreating the substrate with a liquid that promotes rapid and even spreading of the discrete portions of the imprint resist and polymerizes with the imprint resist during formation of the patterned layer.

Spreading of discrete portions of a second liquid on a first liquid may be understood with reference to FIGS. 3A-3D. FIGS. 3A-3D depict first liquid 300 and second liquid 302 on substrate 304 and in contact with gas 306 (e.g., air, an inert gas such as helium or nitrogen, or a combination of inert gases). First liquid 300 is present on substrate 304 in the form of coating or layer, used here interchangeably. In some cases, first liquid 300 is present as a layer having a thickness of a few nanometers (e.g., between 1 nm and 15 nm, or between 5 nm and 10 nm). Second liquid 302 is present in the form of a discrete portion (“drop”). The properties of first liquid 300 and second liquid 302 may vary with respect to each other. For instance, in some cases, first liquid 300 may be more viscous and dense than second liquid 302.

The interfacial surface energy, or surface tension, between second liquid 302 and first liquid 300 is denoted as γ_(L1L2). The interfacial surface energy between first liquid 300 and gas 306 is denoted as γ_(L1G). The interfacial surface energy between second liquid 302 and gas 306 is denoted as γ_(L2G). The interfacial surface energy between first liquid 300 and substrate 304 is denoted as γ_(SL1). The interfacial surface energy between second liquid 302 and substrate 304 is denoted as γ_(SL2).

FIG. 3A depicts second liquid 302 as a drop disposed on first liquid 300. Second liquid 302 does not deform first liquid 300 and does not touch substrate 304. As depicted, first liquid 300 and second liquid 302 do not intermix, and the interface between the first liquid and the second liquid is depicted as flat. At equilibrium, the contact angle of second liquid 302 on first liquid 300 is θ, which is related to the interfacial surface energies γ_(L1G), γ_(L2G), and γ_(L1L2) by Young's equation:

γ_(L1G)=γ_(L1L2)+γ_(L2G)·cos(θ)  (1)

If

γ_(L1G)≧γ_(L1L2)+γ_(L2G)  (2)

then θ=0°, and second liquid 302 spreads completely on first liquid 300. If the liquids are intermixable, then after some elapsed time,

γ_(L1L2)=0  (3)

In this case, the condition for complete spreading of second liquid 302 on first liquid 300 is

γ_(L1G)≧γ_(L2G)  (4)

For thin films of first liquid 300 and small drops of second liquid 302, intermixing may be limited by diffusion processes. Thus, for second liquid 302 to spread on first liquid 300, the inequality (2) is more applicable in the initial stages of spreading, when second liquid 302 is disposed on first liquid 300 in the form of a drop.

FIG. 3B depicts contact angle formation for a drop of second liquid 302 when the underlying layer of first liquid 300 is thick. In this case, the drop does not touch the substrate 304. Drop of second liquid 302 and layer of first liquid 300 intersect at angles α, β, and θ, with

α+β+θ=2π  (5)

There are three conditions for the force balance along each interface:

γ_(L2G)+γ_(L1L2)·cos(θ)+γ_(L1G)·cos(α)=0  (6)

γ_(L2G)·cos(θ)+γ_(L1L2)+γ_(L1G)·cos(β)=0  (7)

γ_(L2G)·cos(α)+γ_(L1L2)·cos(β)+γ_(L1G)=0  (8)

If first liquid 300 and second liquid 302 are intermixable, then

γ_(L1L2)=0  (9)

and equations (6)-(8) become:

γ_(L2G)+γ_(L1G)·cos(α)=0  (10)

γ_(L2G)·cos(θ)+γ_(L1G)·cos(β)=0  (11)

γ_(L2G)·cos(α)+γ_(L1G)=0  (12)

Equations (10) and (12) give

cos²(α)=1  (13)

and

α=0,π  (14)

When second liquid 302 wets first liquid 300,

α=π  (15)

γ_(L2G)=γ_(L1G)  (16)

and equation (11) gives

cos(θ)+cos(β)=0  (17)

Combining this result with equations (5) and (15) gives:

θ=0  (18)

β=π  (19)

Thus, equations (15), (18), and (19) give solutions for angles α, β, and θ.

When

γ_(L1G)≧γ_(L2G)(20)

there is no equilibrium between the interfaces. Equation (12) becomes an inequality even for α=π, and second liquid 302 spreads continuously on first liquid 300.

FIG. 3C depicts a more complex geometry for a drop of second liquid 302 touching substrate 304 while also having an interface with first liquid 300. Interfacial regions between first liquid 300, second liquid 302, and gas 306 (defined by angles α, β, and θ₁) and first liquid 300, second liquid 302, and substrate 304 (defined by angle θ₂) must be considered to determine spreading behavior of the second liquid on the first liquid.

The interfacial region between first liquid 300, second liquid 302, and gas 306 is governed by equations (6)-(8). Since first liquid 300 and second liquid 302 are intermixable,

γ_(L1L2)=0  (21)

The solutions for angle α are given by equation (14). In this case, let

α=0  (22)

and

θ₁=π  (23)

β=π  (24)

When

γ_(L1G)≧γ_(L2G)  (25)

there is no equilibrium between the drop of second liquid 302 and first liquid 300, and the drop spreads continuously along the interface between the second liquid and the gas until limited by other physical limitations (e.g., conservation of volume and intermixing).

For the interfacial region between first liquid 300, second liquid 302, and substrate 304, an equation similar to equation (1) should be considered:

γ_(SL1)=γ_(SL2)+γ_(L1L2)·cos(θ₂)  (26)

If

γ_(SL1)≧γ_(SL2)+γ_(L1L2)  (27)

the drop spreads completely, and θ₂=0.

Again, as for the intermixable liquids, the second term γ_(L1L2)=0, and the inequality (27) simplifies to

γ_(SL1)≦γ_(SL2)  (28)

The combined condition for the drop spreading is expressed as

γ_(L1G)+γ_(SL1)≧γ_(L2G)+γ_(SL2)  (29)

when energies before and after the spreading are considered. There should be an energetically favorable transition (i.e., the transition that minimizes the energy of the system).

Different relationships between the four terms in the inequality (29) will determine the drop spreading character. The drop of second liquid 302 can initially spread along the surface of the first liquid 300 if the inequality (25) is valid but the inequality (28) is not. Or the drop can start spreading along liquid-solid interface provided the inequality (28) holds up and the inequality (25) does not. Eventually first liquid 300 and second liquid 302 will intermix, thus introducing more complexity.

FIG. 3D depicts a geometry for a drop of second liquid 302 touching substrate 304 while having an interface with first liquid 300. As indicated in FIG. 3D, there are two interfacial regions of interest on each side of the drop of second liquid 302. The first interfacial region is where first liquid 300, second liquid 302, and gas 306 meet, indicated by angles α, β, and θ₁. The second interfacial region of interest is where first liquid 300, second liquid 302, and substrate 304 meet, indicated by angle θ₂. Here, θ₁ approaches 0° and θ₂ approaches 180° as the drop spreads when the surface tension of the interface between second liquid 302 and substrate 304 exceeds the surface tension of the interface between first liquid 300 and the substrate (γ_(SL2)≧γ_(SL1)). That is, drop of second liquid 302 spreads along the interface between first liquid 300 and the second liquid and does not spread along the interface between the second liquid and substrate 304.

For the interface between first liquid 300, second liquid 302, and gas 306, equations (6)-(8) are applicable. First liquid 300 and second liquid 302 are intermixable, so

γ_(L1L2)=0  (30)

The solutions for angle α are given by equation (14). For

α=π  (31)

Equation (11) gives

cos(θ₁)+cos(β)=0  (32)

and

θ₁=0  (33)

β=π  (34)

When

γ_(L1G)≦γ_(L2G)  (35)

there is no equilibrium between the drop of second liquid 302 and liquid 300, and the drop spreads continuously along the interface between the second liquid and the gas until limited by other physical limitations (e.g., conservation of volume and intermixing).

For the interfacial region between second liquid 302 and substrate 304,

$\begin{matrix} {\gamma_{{SL}\; 1} = {\gamma_{{SL}\; 2} + {\gamma_{L\; 1L\; 2} \cdot {\cos \left( \theta_{2} \right)}}}} & (36) \\ {{{\cos \left( \theta_{2} \right)} = \frac{\gamma_{{SL}\; 1} - \gamma_{{SL}\; 2}}{\gamma_{L\; 1L\; 2}}}{If}} & (37) \\ {\gamma_{{SL}\; 1} \leq \gamma_{{SL}\; 2}} & (38) \end{matrix}$

and the liquids are intermixable, i.e.,

γ_(L1L2)→0  (39)

−∞≦cos(θ₂)≦−1  (40)

the angle θ₂ approaches 180° and then becomes undefined. That is, second liquid 302 has a tendency to contract along the substrate interface and spread along the interface between first liquid 300 and gas 306.

Spreading of second liquid 302 on first liquid 300 can be summarized for three different cases, along with the surface energy relationship for complete spreading. In the first case, drop of second liquid 302 is disposed on layer of first liquid 300, and the drop of the second liquid does not contact substrate 304. Layer of first liquid 300 can be thick or thin, and the first liquid 300 and second liquid 302 are intermixable. Under ideal conditions, when the surface energy of first liquid 300 in the gas 306 is greater than or equal to the surface energy of the second liquid 302 in the gas (γ_(L1G)≧γ_(L2G)), complete spreading of the drop of second liquid 302 occurs on layer of first liquid 300. In the second case, drop of second liquid 302 is disposed on layer of first liquid 300 while touching and spreading at the same time on substrate 304. The first liquid and second liquid 302 are intermixable. Under ideal conditions, complete spreading occurs when: (i) the surface energy of first liquid 300 in the gas is greater than or equal to the surface energy of second liquid 302 in the gas (γ_(L1G)≧γ_(L2G)); and (ii) the surface energy of the interface between the first liquid and substrate 304 exceeds the surface energy of the interface between the second liquid and the substrate (γ_(SL1)≧γ_(SL2)). In the third case, drop of second liquid 302 is disposed on layer of the first liquid 300 while touching substrate 304. Spreading may occur along the interface between second liquid 302 and first liquid 300 or the interface between the second liquid and substrate 304. The first liquid and second liquid 302 are intermixable. Under ideal conditions, complete spreading occurs when the sum of the surface energy of first liquid 300 in the gas and the surface energy of the interface between the first liquid and substrate 304 is greater than or equal to the sum of the surface energy of second liquid 302 in the gas and the surface energy of the interface between the second liquid and the substrate (γ_(L1G)+γ_(SL1)≧γ_(L2G)+γ_(SL2)) while the surface energy of first liquid 300 in the gas is greater than or equal to the surface energy of second liquid 302 in the gas (γ_(L1G)≧γ_(L2G)) or (ii) the surface energy of the interface between the first liquid and substrate 304 exceeds the surface energy of the interface between the second liquid and the substrate (γ_(SL1)≧γ_(SL2)).

By pretreating a nanoimprint lithography substrate with a liquid selected to have a surface energy greater than that of the imprint resist in the ambient atmosphere (e.g., air or an inert gas), the rate at which an imprint resist spreads on the substrate in a drop-on-demand nanoimprint lithography process may be increased and a more uniform thickness of the imprint resist on the substrate may be established before the imprint resist is contacted with the template, thereby facilitating throughput in the nanoimprint lithography process. If the pretreatment composition includes polymerizable components capable of intermixing with the imprint resist, then this can advantageously contribute to formation of the resulting polymeric layer without the addition of undesired components, and may result in more uniform curing, thereby providing more uniform mechanical and etch properties.

FIG. 4 is a flowchart showing a process 400 for facilitating throughput in drop-on-demand nanoimprint lithography. Process 400 includes operations 402-410. In operation 402, a pretreatment composition is disposed on a nanoimprint lithography substrate to form a pretreatment coating on the substrate. In operation 404, discrete portions (“drops”) of an imprint resist are disposed on the pretreatment coating, with each drop covering a target area of the substrate. The pretreatment composition and the imprint resist are selected such that the interfacial surface energy between the pretreatment composition and the air exceeds the interfacial surface energy between the imprint resist and the air.

In operation 406, a composite polymerizable coating (“composite coating”) is formed on the substrate as each drop of the imprint resist spreads beyond its target area. The composite coating includes a homogeneous or inhomogeneous mixture of the pretreatment composition and the imprint resist. In operation 408, the composite coating is contacted with a nanoimprint lithography template (“template”), and allowed to spread and fill all the volume between the template and substrate, and in operation 410, the composite coating is polymerized to yield a polymeric layer on the substrate. After polymerization of the composite coating, the template is separated from the polymeric layer, leaving a nanoimprint lithography stack. As used herein, “nanoimprint lithography stack” generally refers to the substrate and the polymeric layer adhered to the substrate, each or both of which may include one or more additional (e.g., intervening) layers. In one example, the substrate includes a base and an adhesion layer adhered to the base.

In process 400, the pretreatment composition and the imprint resist may include a mixture of components as described, for example, in U.S. Pat. No. 7,157,036 and U.S. Pat. No. 8,076,386, as well as Chou et al. 1995, Imprint of sub-25 nm vias and trenches in polymers. Applied Physics Letters 67(21):3114-3116; Chou et al. 1996, Nanoimprint lithography. Journal of Vacuum Science Technology B 14(6): 4129-4133; and Long et al. 2007, Materials for step and flash imprint lithography (S-FIL®. Journal of Materials Chemistry 17:3575-3580, all of which are incorporated by reference herein. Suitable compositions include polymerizable monomers (“monomers”), crosslinkers, resins, photoinitiators, surfactants, or any combination thereof. Classes of monomers include acrylates, methacrylates, vinyl ethers, and epoxides, as well as polyfunctional derivatives thereof. In some cases, the pretreatment composition, the imprint resist, or both are substantially free of silicon. In other cases, the pretreatment composition, the imprint resist, or both are silicon-containing. Silicon-containing monomers include, for example, siloxanes and disiloxanes. Resins can be silicon-containing (e.g., silsesquioxanes) and non-silicon-containing (e.g., novolak resins). The pretreatment composition, the imprint resist, or both may also include one or more polymerization initiators or free radical generators. Classes of polymerization initiators include, for example, photoinitiators (e.g., acyloins, xanthones, and phenones), photoacid generators (e.g., sulfonates and onium salts), and photobase generators (e.g., ortho-nitrobenzyl carbamates, oxime urethanes, and O-acyl oximes).

Suitable monomers include monofunctional, difunctional, or multifunctional acrylates, methacrylates, vinyl ethers, and epoxides, in which mono-, di-, and multi-refer to one, two, and three or more of the indicated functional groups, respectively. Some or all of the monomers may be fluorinated (e.g., perfluorinated). In the case of acrylates, for example, the pretreatment, the imprint resist, or both may include one or more monofunctional acrylates, one or more difunctional acrylates, one or more multifunctional acrylates, or a combination thereof.

Examples of suitable monofunctional acrylates include isobornyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, dicyclopentenyl acrylate, benzyl acrylate, 1-naphthyl acrylate, 4-cyanobenzyl acrylate, pentafluorobenzyl acrylate, 2-phenylethyl acrylate, phenyl acrylate, (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl acrylate, n-hexyl acrylate, 4-tert-butylcyclohexyl acrylate, methoxy polyethylene glycol (350) monoacrylate, and methoxy polyethylene glycol (550) monoacrylate.

Examples of suitable diacrylates include ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (e.g., Mn, avg=575), 1,2-propanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 2-butene-1,4-diacrylate, 1,3-butylene glycol diacrylate, 3-methyl-1,3-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, 1H,1H,6H,6H-perfluoro-1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate, 1,12-dodecanediol diacrylate, neopentyl glycol diacrylate, cyclohexane dimethanol diacrylate, tricyclodecane dimethanol diacrylate, bisphenol A diacrylate, ethoxylated bisphenol A diacrylate, m-xylylene diacrylate, ethoxylated (3) bisphenol A diacrylate, ethoxylated (4) bisphenol A diacrylate, ethoxylated (10) bisphenol A diacrylate, tricyclodecane dimethanol diacrylate, 1,2-adamantanediol diacrylate, 2,4-diethylpentane-1,5-diol diacrylate, poly(ethylene glycol) (400) diacrylate, poly(ethylene glycol) (300) diacrylate, 1,6-hexanediol (EO)₂ diacrylate, 1,6-hexanediol (EO)₅ diacrylate, and alkoxylated aliphatic diacrylate ester.

Examples of suitable multifunctional acrylates include trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate (e.g., propoxylated (3) trimethylolpropane triacrylate, propoxylated (6) trimethylolpropane triacrylate), trimethylolpropane ethoxylate triacrylate (e.g., n˜1.3, 3, 5), di(trimethylolpropane) tetraacrylate, propoxylated glyceryl triacrylate (e.g., propoxylated (3) glyceryl triacrylate), tris (2-hydroxy ethyl) isocyanurate triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, ethoxylated pentaerythritol tetracrylate, dipentaerythritol pentaacrylate, tripentaerythritol octaacrylate.

Examples of suitable crosslinkers include difunctional acrylates and multifunctional acrylates, such as those described herein.

Examples of suitable photoinitiators include IRGACURE 907, IRGACURE 4265, 651, 1173, 819, TPO, and TPO-L.

A surfactant can be applied to a patterned surface of an imprint lithography template, added to an imprint lithography resist, or both, to reduce the separation force between the solidified resist and the template, thereby reducing separation defects in imprinted patterns formed in an imprint lithography process and to increase the number of successive imprints that can be made with an imprint lithography template. Factors in selecting a release agent for an imprint resist include, for example, affinity with the surface and desired surface properties of the treated surface.

Examples of suitable surfactants include fluorinated and non-fluorinated surfactants. The fluorinated and non-fluorinated surfactants may be ionic or non-ionic surfactants. Suitable non-ionic fluorinated surfactants include fluoro-aliphatic polymeric esters, perfluoroether surfactants, fluorosurfactants of polyoxyethylene, fluorosurfactants of polyalkyl ethers, fluoroalkyl polyethers, and the like. Suitable non-ionic non-fluorinated surfactants include ethoxylated alcohols, ethoxylated alkylphenols, and polyethyleneoxide-polypropyleneoxide block copolymers.

Exemplary commercially available surfactant components include, but are not limited to, ZONYL® FSO and ZONYL® FS-300, manufactured by E.I. du Pont de Nemours and Company having an office located in Wilmington, Del.; FC-4432 and FC-4430, manufactured by 3M having an office located in Maplewood, Minn.; MASURF® FS-1700, FS-2000, and FS-2800 manufactured by Pilot Chemical Company having an office located in Cincinnati, Ohio; S-107B, manufactured by Chemguard having an office located in Mansfield, Tex.; FTERGENT 222F, FTERGENT 250, FTERGENT 251, manufactured by NEOS Chemical Chuo-ku, Kobe-shi, Japan; PolyFox PF-656, manufactured by OMNOVA Solutions Inc. having an office located in Akron, Ohio; Pluronic L35, L42, L43, L44, L63, L64, etc. manufactured by BASF having an office located in Florham Park, N.J.; Brij 35, 58, 78, etc. manufactured by Croda Inc. having an office located in Edison, N.J.

In some examples, an imprint resist includes 0 wt % to 80 wt % (e.g., 20 wt % to 80 wt % or 40 wt % to 80 wt %) of one or more monofunctional acrylates; 90 wt % to 98 wt % of one or more difunctional or multifunctional acrylates (e.g., the imprint resist may be substantially free of monofunctional acrylates) or 20 wt % to 75 wt % of one or more difunctional or multifunctional acrylates (e.g., when one or more monofunctional acrylates is present); 1 wt % to 10 wt % of one or more photoinitiators; and 1 wt % to 10 wt % of one or more surfactants. In one example, an imprint resist includes about 40 wt % to about 50 wt % of one or more monofunctional acrylates, about 45 wt % to about 55 wt % of one or more difunctional acrylates, about 4 wt % to about 6 wt % of one or more photoinitiators, and about 3 wt % surfactant. In another example, an imprint resist includes about 44 wt % of one or more monofunctional acrylates, about 48 wt % of one or more difunctional acrylates, about 5 wt % of one or more photoinitiators, and about 3 wt % surfactant. In yet another example, an imprint resist includes about 10 wt % of a first monofunctional acrylate (e.g., isobornyl acrylate), about 34 wt % of a second monofunctional acrylate (e.g., benzyl acrylate) about 48 wt % of a difunctional acrylate (e.g., neopentyl glycol diacrylate), about 2 wt % of a first photoinitiator (e.g., IRGACURE TPO), about 3 wt % of a second photoinitiator (e.g., DAROCUR 4265), and about 3 wt % surfactant. Examples of suitable surfactants include X—R—(OCH₂CH₂)_(n)OH, where R=alkyl, aryl, or poly(propylene glycol), X═H or —(OCH₂CH₂)_(n)OH, and n is an integer (e.g., 2 to 20, 5 to 15, or 10 to 12) (e.g., X═—(OCH₂CH₂)_(n)OH, R=poly(propylene glycol), and n=10 to 12); Y—R—(OCH₂CH₂)_(n)OH, where R=alkyl, aryl, or poly(propylene glycol), Y=a fluorinated chain (perfluorinated alkyl or perfluorinated ether) or poly(ethylene glycol) capped with a fluorinated chain, and n is an integer (e.g., 2 to 20, 5 to 15, or 10 to 12) (e.g., Y=poly(ethylene glycol) capped with a perfluorinated alkyl group, R=poly(propylene glycol), and n=10 to 12); and a combination thereof. The viscosity of the imprint resist is typically between 0.1 cP and 25 cP, or between 5 cP and 15 cP at 23° C. The interfacial surface energy between the imprint resist and air is typically between 20 mN/m and 36 mN/m.

In one example, a pretreatment composition includes 0 wt % to 80 wt % (e.g., 20 wt % to 80 wt % or 40 wt % to 80 wt %) of one or more monofunctional acrylates; 90 wt % to 100 wt % of one or more difunctional or multifunctional acrylates (e.g., the pretreatment composition is substantially free of monofunctional acrylates) or 20 wt % to 75 wt % of one or more difunctional or multifunctional acrylates (e.g., when one or more monofunctional acrylates is present); 0 wt % to 10 wt % of one or more photoinitiators; and 0 wt % to 10 wt % of one or more surfactants.

The pretreatment composition is typically miscible with the imprint resist. The pretreatment composition typically has a low vapor pressure, such that it remains present as a thin film on the substrate until the composite coating is polymerized. In one example, the vapor pressure of a pretreatment composition is less than 1×10⁻⁴ mmHg at 25° C. The pretreatment composition also typically has a low viscosity to facilitate rapid spreading of the pretreatment composition on the substrate. In one example, the viscosity of a pretreatment composition is less than 90 cP at 23° C. The interfacial surface energy between the pretreatment composition and air is typically between 30 mN/m and 45 mN/m. The pretreatment composition is typically selected to be chemically stable, such that decomposition does not occur during use.

A pretreatment composition may be a single polymerizable component (e.g., a monomer such as a monofunctional acrylate, a difunctional acrylate, or a multifunctional acrylate), a mixture of two or more polymerizable components (e.g., a mixture of two or more monomers), or a mixture of one or more polymerizable components and one or more other components (e.g., a mixture of monomers; a mixture of two or more monomers and a surfactant, a photoinitiator, or both; and the like). In some examples, a pretreatment composition includes trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, 1,12-dodecanediol diacrylate, poly(ethylene glycol) diacrylate, tetraethylene glycol diacrylate, 1,3-adamantanediol diacrylate, nonanediol diacrylate, m-xylylene diacrylate, tricyclodecane dimethanol diacrylate, or any combination thereof.

Mixtures of polymerizable components may result in synergistic effects, yielding pretreatment compositions having a more advantageous combination of properties (e.g., low viscosity, good etch resistance and film stability) than a pretreatment composition with a single polymerizable component. In one example, the pretreatment composition is a mixture of 1,12-dodecanediol diacrylate and tricyclodecane dimethanol diacrylate. In another example, the pretreatment composition is a mixture of tricyclodecane dimethanol diacrylate and tetraethylene glycol diacrylate. The pretreatment composition is generally selected such that one or more components of the pretreatment composition polymerizes (e.g., covalently bonds) with one or more components of the imprint resist during polymerization of the composite polymerizable coating. In some cases, the pretreatment composition includes a polymerizable component that is also in the imprint resist, or a polymerizable component that has a functional group in common with one or more polymerizable components in the imprint resist (e.g., an acrylate group). Suitable examples of pretreatment compositions include multifunctional acrylates such as those described herein, including propoxylated (3) trimethylolpropane triacrylate, trimethylolpropane triacrylate, and dipentaerythritol pentaacrylate.

A pretreatment composition is typically selected such that the interfacial surface energy at an interface between the pretreatment and air exceeds that of the imprint resist used in conjunction with the pretreatment composition, thereby promoting rapid spreading of the liquid imprint resist on the liquid pretreatment composition to form a uniform composite coating on the substrate before the composite coating is contacted with the template. The interfacial surface energy between the pretreatment composition and air typically exceeds that between the imprint resist and air or between at least a component of the imprint resist and air by at least 0.5 mN/m or at least 1 mN/m up to 25 mN/m (e.g., 0.5 mN/m to 25 mN/m, 0.5 mN/m to 15 mN/m, 0.5 mN/m to 7 mN/m, 1 mN/m to 25 mN/m, 1 mN/m to 15 mN/m, or 1 mN/m to 7 mN/m, although these ranges may vary based on chemical and physical properties of the pretreatment composition and the imprint resist and the resulting interaction between these two liquids. When the difference between surface energies is too low, limited spreading of the imprint resist results, and the drops maintain a spherical cap-like shape and remain separated by the pretreatment composition. When the difference between surface energies is too high, excessive spreading of the imprint resist results, with most of the imprint resist moving toward the adjacent drops, emptying the drop centers, such that the composite coating has convex regions above the drop centers. Thus, when the difference between surface energies is too low or too high, the resulting composite coating is nonuniform, with significant concave or convex regions. When the difference in surface energies is appropriately selected, the imprint resist spreads quickly to yield a substantially uniform composite coating. Advantageous selection of the pretreatment composition and the imprint resist allows fill time to be reduced by 50-90%, such that filling can be achieved in as little as 1 sec, or in some cases even as little as 0.1 sec.

To achieve these advantages related to improved throughput associated with the surface tension gradient between the pretreatment composition and the imprint resist, the pretreatment composition and the imprint resist differ in surface energy, and therefore composition. Complete mixing of the pretreatment composition and the imprint resist is difficult to achieve given the short spreading time of the imprint resist needed for high throughput processing. As such, the distribution of the pretreatment composition and the imprint resist across the imprint field is typically non-uniform (i.e., the pretreatment composition is typically pushed to the drop boundary areas due to the nature of the spreading mechanism). There can be non-uniform distributions of the types of monomers, the relative amounts of monofunctional and multifunctional monomers, and the concentration of photoinitiators and/or other additives (e.g., sensitizers or surfactants). These non-uniformities can affect the composition and also the extent of curing, both of which impact the resulting etch rate of the composite coating.

After polymerization of the composite coating, a non-uniform composition or extent of curing may cause non-uniform etching across the field, thereby resulting in poor critical dimension uniformity or incomplete etching. As described herein, etch uniformity may be promoted by minimizing the variation in etch rate across a composite polymeric layer formed from a pretreatment composition and an imprint resist (e.g., by “matching the etch rate”). As used herein, “etch rate” generally refers to the thickness of material etched divided by the etching time (typically with units, nm/s). A measure of matching etch rates includes comparing the variation in pre-etch height and post-etch height in a composite polymeric layer formed by a nanoimprint process. In one example, a variation in post-etch height across a composite polymeric layer is less than or equal to a variation in pre-etch height across a composite polymeric layer. In some cases, the variation in pre-etch height is ±20% or ±10% of the pre-etch average height of a composite polymeric layer, and a variation in post-etch height is ±10% of the post-etch average height of the composite polymeric layer. In certain cases, the variation in pre-etch height is ±5% of the pre-etch average height of a composite polymeric layer, and a variation in post-etch height is ±5% of the post-etch average height of the composite polymeric layer.

As described herein, etching may be achieved by any of a number of processes known in the art, including oxygen- or halogen-containing plasma chemistries using reactive ion etching or high density etching (e.g., inductively coupled plasma reactive ion etching, magnetically enhanced reactive ion etching, transmission coupled plasma etching, or the like). To achieve etch uniformity, the composition of the pretreatment composition and the imprint resist may be selected to minimize the difference between the etch rate of the pretreatment composition and the etch rate of the imprint resist. While the pretreatment composition and the imprint resist may have some desired properties in common (e.g., low viscosity, rapid curing, mechanical strength), different constraints for the pretreatment composition and the imprint resist make it challenging to match etch rate. In particular, a desirable pretreatment composition has low volatility and a higher surface tension than the imprint resist. Low volatility of the pretreatment composition typically imparts stability over a relatively long period of time on the substrate prior to imprinting. In contrast, the imprint resist is typically dispensed and then imprinted in less than one second, so the requirement for low volatility is typically relaxed for the imprint resist relative to the pretreatment composition.

Monomers having at least one of higher molecular mass and higher intermolecular forces typically demonstrate low volatility. Thus, pretreatment compositions generally include higher molecular mass multifunctional monomers (e.g., multifunctional acrylates) and are typically free of the more volatile monofunctional acrylates found in imprint resists. As used herein, “higher molecular mass” typically refers to a molecular mass of at least 250 Da or at least 300 Da. A high percentage of multifunctional monomers in a pretreatment composition may result in more extensive crosslinking than found in typical imprint resists, and more extensive crosslinking may impart higher etch resistance, and thus a lower etch rate.

Monomers with relatively strong intermolecular forces are also associated with low volatility. Monomers with larger polarity and, especially those capable of hydrogen bonding, generally have higher intermolecular forces and, therefore demonstrate lower volatility. Monomers with greater polarity may also advantageously promote higher surface tension. In some cases, greater polarity is due, at least in part, to the presence of more oxygen atoms in the molecule (e.g., in the form of ethylene glycol units, hydroxyl groups, carboxyl groups, and the like). While often contributing to strong intermolecular forces and higher surface tension, the presence of oxygen atoms also tends to reduce etch resistance and thus increase etch rate. Thus, a pretreatment composition typically includes monomers having lower etch resistance and a higher etch rate than monomers in an imprint resist.

With respect to viscosity, an imprint resist is generally more constrained than a pretreatment composition, since the imprint resist is typically dispensed via inkjet. This method of application may set an upper limit on viscosity of the imprint resist. To achieve low viscosity, the imprint resist will typically include a greater amount of small, low molecular weight monomers (e.g., monofunctional acrylates) than the pretreatment composition. While it may be advantageous for a pretreatment composition to have a low viscosity, other constraints (e.g., low volatility) typically result in higher viscosity for a pretreatment composition than an imprint resist. As with surface tension and volatility, viscosity is also closely related to intermolecular forces, and greater intermolecular forces contribute to higher viscosity. On the other hand, a pretreatment composition can be applied by spin coating, which relaxes the upper limit on viscosity relative to the imprint resist. As a result, the viscosity of a pretreatment composition can be at least 1.5 times, 2 times, 10 times, or 50 times higher than that of an imprint resist.

Thus, constraints related to volatility, surface tension, and viscosity of a pretreatment composition and an imprint resist typically result in an imprint resist having a lower etch rate than a pretreatment composition in terms of chemical composition. However, the difference in etch rate between a pretreatment composition and an imprint resist may be reduced by a higher percentage of multifunctional monomers (crosslinkers) in a pretreatment composition (i.e., a lower etch rate of the pretreatment composition). To minimize the difference between the etch rate of a pretreatment composition and an imprint resist, the pretreatment composition may be selected to include one or more high etch resistance monomers, a high percentage of multifunctional monomers, or a combination thereof.

Examples of higher etch resistance monomers include tricyclodecanedimethanol diacrylate, 1,3-adamantanediol diacrylate, m-xylylene diacrylate, p-xylylene diacrylate, 2-phenyl-1,3-propanediol diacrylate, phenylethyleneglycol diacrylate, 1,9-nonanediol diacrylate, 1,12-dodecanediol diacrylate, and trimethylolpropane triacrylate. Estimates of the etch resistance or etch rate of each material can be made using composition- or structure-based parameters, such as the Ohnishi number or the ring parameter. The Ohnishi number is equal to the total number of atoms in a polymer repeat unit divided by the difference between the number of carbon atoms and the number of oxygen atoms: Ohnishi number=N_(total)/(N_(carbon)−N_(oxygen)). The ring parameter is equal to the mass of the resist existing as carbon atoms in a ring structure, M_(CR), divided by the total resist mass, M_(TOT): ring parameter r=M_(CR)/M_(TOT).

The ratios of the Ohnishi numbers calculated for different pretreatment compositions are listed in Table 2. However, these parameters are empirical and have limited accuracy; more accurate values for etch rate are typically obtained experimentally. Experimentally determined etch rate for a pretreatment composition is typically lower than that predicted based on the Ohnishi number. Thus, it may be advantageous to increase the etch resistance or lower the etch rate of an imprint resist to match that of a pretreatment composition. Due to the low viscosity constraints of the imprint resist, small aromatic monomers may be suitable for increasing etch resistance or lowering etch rate while maintaining low viscosity. Exemplary low viscosity, high etch resistance monomers include benzyl acrylate, m-xylylene diacrylate, p-xylylene diacrylate, 2-phenyl-1,3-propanediol diacrylate, and phenylethyleneglycol diacrylate.

Referring to operation 402 of process 400, FIG. 5A depicts substrate 102 including base 500 and adhesion layer 502. Base 500 is typically a silicon wafer. Other suitable materials for base 500 include fused silica, quartz, silicon germanium, gallium arsenide, and indium phosphide. Adhesion layer 502 serves to increase adhesion of the polymeric layer to base 500, thereby reducing formation of defects in the polymeric layer during separation of the template from the polymeric layer after polymerization of the composite coating. A thickness of adhesion layer 502 is typically between 1 nm and 10 nm. Examples of suitable materials for adhesion layer 502 include those disclosed in U.S. Pat. Nos. 7,759,407; 8,361,546; 8,557,351; 8,808,808; and 8,846,195, all of which are incorporated by reference herein. In one example, an adhesion layer is formed from a composition including ISORAD 501, CYMEL 303ULF, CYCAT 4040 or TAG 2678 (a quaternary ammonium blocked trifluoromethanesulfonic acid), and PM Acetate (a solvent consisting of 2-(1-methoxy)propyl acetate available from Eastman Chemical Company of Kingsport, Tenn.). In some cases, substrate 102 includes one or more additional layers between base 500 and adhesion layer 502. In certain cases, substrate 102 includes one or more additional layers on adhesion layer 502. For simplicity, substrate 102 is depicted as including only base 500 and adhesion layer 502.

FIG. 5B depicts pretreatment composition 504 after the pretreatment composition has been disposed on substrate 102 to form pretreatment coating 506. As depicted in FIG. 5B, pretreatment coating 506 is formed directly on adhesion layer 502 of substrate 102. In some cases, pretreatment coating 506 is formed on another surface of substrate 102 (e.g., directly on base 500). Pretreatment coating 506 is formed on substrate 102 using techniques such as spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD). In the case of, for example, spin-coating or dip coating and the like, the pretreatment composition can be dissolved in one or more solvents (e.g., propylene glycol methyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), and the like) for application to the substrate, with the solvent then evaporated away to leave the pretreatment coating. A thickness t_(p) of pretreatment coating 506 is typically between 1 nm and 100 nm (e.g., between 1 nm and 50 nm, between 1 nm and 25 nm, or between 1 nm and 10 nm).

Referring again to FIG. 4, operation 404 of process 400 includes disposing drops of imprint resist on the pretreatment coating, such that each drop of the imprint resist covers a target area of the substrate. A volume of the imprint resist drops is typically between 0.6 pL and 30 pL, and a distance between drop centers is typically between 35 μm and 350 μm. In some cases, the volume ratio of the imprint resist to the pretreatment is between 1:1 and 15:1. In operation 406, a composite coating is formed on the substrate as each drop of the imprint resist spreads beyond its target area, forming a composite coating. As used herein, “prespreading” refers to the spontaneous spreading of the drops of imprint resist that occurs between the time when the drops initially contact the pretreatment coating and spread beyond the target areas, and the time when the template contacts the composite coating.

FIGS. 6A-6D depict top-down views of drops of imprint resist on pretreatment coating at the time of disposal of the drops on target areas, and of the composite coating before, during, and at the end of drop spreading. Although the drops are depicted in a square grid, the drop pattern is not limited to square or geometric patterns.

FIG. 6A depicts a top-down view of drops 600 on pretreatment coating 506 at the time when the drops are initially disposed on the pretreatment coating, such that the drops cover but do not extend beyond target areas 602. After drops 600 are disposed on pretreatment coating 506, the drops spread spontaneously to cover a surface area of the substrate larger than that of the target areas, thereby forming a composite coating on the substrate. FIG. 6B depicts a top-down view of composite coating 604 during prespreading (after some spreading of drops 600 beyond the target areas 602), and typically after some intermixing of the imprint resist and the pretreatment. As depicted, composite coating 604 is a mixture of the liquid pretreatment composition and the liquid imprint resist, with regions 606 containing a majority of imprint resist (“enriched” with imprint resist), and regions 608 containing a majority of pretreatment (“enriched” with pretreatment). As prespreading progresses, composite coating 604 may form a more homogeneous mixture of the pretreatment composition and the imprint resist.

Spreading may progress until one or more of regions 606 contacts one or more adjacent regions 606. FIGS. 6C and 6D depict composite coating 604 at the end of spreading. As depicted in FIG. 6C, each of regions 606 has spread to contact each adjacent region 606 at boundaries 610, with regions 608 reduced to discrete (non-continuous) portions between regions 606. In other cases, as depicted in FIG. 6D, regions 606 spread to form a continuous layer, such that regions 608 are not distinguishable. In FIG. 6D, composite coating 604 may be a homogenous mixture of the pretreatment composition and the imprint resist.

FIGS. 7A-7D are cross-sectional views along lines w-w, x-x, y-y, and z-z of FIGS. 6A-D, respectively. FIG. 7A is a cross-sectional view along line w-w of FIG. 6A, depicting drops of imprint resist 600 covering a surface area of substrate 102 corresponding to target areas 602. Each target area (and each drop as initially disposed) has a center as indicated by line c-c, and line b-b indicates a location equidistant between the centers of two target areas 602. For simplicity, drops 600 are depicted as contacting adhesion layer 502 of substrate 102, and no intermixing of the imprint resist and the pretreatment composition is depicted. FIG. 7B is a cross-sectional view along line x-x of FIG. 6B, depicting composite coating 604 with regions 608 exposed between regions 606, after regions 606 have spread beyond target areas 602. FIG. 7C is a cross-sectional view along line y-y of FIG. 6C at the end of prespreading, depicting composite coating 604 as a homogeneous mixture of the pretreatment composition and imprint resist. As depicted, regions 606 have spread to cover a greater surface of the substrate than in FIG. 7B, and regions 608 are correspondingly reduced. Regions 606 originating from drops 600 are depicted as convex, however, composite coating 604 may be substantially planar or include concave regions. In certain cases, prespreading may continue beyond that depicted in FIG. 7C, with the imprint resist forming a continuous layer over the pretreatment (with no intermixing or with full or partial intermixing). FIG. 7D is a cross-sectional view along line z-z of FIG. 6D, depicting composite coating 604 as a homogenous mixture of the pretreatment composition and the imprint resist at the end of spreading, with concave regions of the composite coating about drop centers cc meeting at boundaries 610, such that the thickness of the polymerizable coating at the drop boundaries exceeds the thickness of the composite coating of the drop centers. As depicted in FIGS. 7C and 7D, a thickness of composite coating 604 at a location equidistant between the centers of two target areas may differ from a thickness of the composite coating at the center of one of the two target areas when the composite coating is contacted with the nanoimprint lithography template.

Referring again to FIG. 4, operations 408 and 410 of process 400 include contacting the composite coating with a template, and polymerizing the composite coating to yield a nanoimprint lithography stack having a composite polymeric layer on the nanoimprint lithography substrate, respectively.

In some cases, as depicted in FIGS. 7C and 7D, composite coating 604 is a homogeneous mixture or substantially homogenous mixture (e.g., at the air-composite coating interface) at the end of prespreading (i.e., just before the composite coating is contacted with the template). As such, the template contacts a homogenous mixture, with a majority of the mixture typically derived from the imprint resist. Thus, the release properties of the imprint resist would generally govern the interaction of the composite coating with the template, as well as the separation of the polymeric layer from the template, including defect formation (or absence thereof) due to separation forces between the template and the polymeric layer.

As depicted in FIGS. 8A and 8B, however, composite coating 604 may include regions 608 and 606 that are enriched with the pretreatment composition and enriched with the imprint resist, respectively, such that template 110 contacts regions of composite coating 604 having different physical and chemical properties. For simplicity, the imprint resist in regions 606 is depicted as having displaced the pretreatment coating, such that regions 606 are in direct contact with the substrate, and no intermixing is shown. Thus, the pretreatment composition in regions 608 is non-uniform in thickness. In FIG. 8A, the maximum height p of regions 606 exceeds the maximum height i of the pretreatment composition, such that template 110 primarily contacts regions 606. In FIG. 8B maximum height i of regions 608 exceeds the maximum height p of the imprint resist, such that template 110 primarily contacts regions 608. Thus, separation of template 110 from the resulting composite polymeric layer and the defect density associated therewith is nonuniform and based on the different interactions between the template and the imprint resist and between the template and the pretreatment composition. Thus, for certain pretreatment compositions (e.g., pretreatment compositions that include a single monomer or a mixture of two or more monomers, but no surfactant), it may be advantageous for the composite coating to form a homogenous mixture, or at least a substantially homogenous mixture at the gas-liquid interface at which the template contacts the composite coating.

FIGS. 9A-9C and 10A-10C are cross-sectional views depicting template 110 and composite coating 604 on substrate 102 having base 500 and adhesion layer 502 before and during contact of the composite coating with the template, and after separation of the template from the composite polymeric layer to yield a nanoimprint lithography stack. In FIGS. 9A-9C, composite coating 604 is depicted as a homogeneous mixture of the pretreatment composition and the imprint resist. In FIGS. 10A-10C, composite coating 604 is depicted as an inhomogeneous mixture of the pretreatment composition and the imprint resist.

FIG. 9A depicts a cross-sectional view of initial contact of template 110 with homogeneous composite coating 900 on substrate 102. In FIG. 9B, template 110 has been advanced toward substrate 102 such that composite coating 900 fills recesses of template 110. After polymerization of composite coating 900 to yield a homogeneous polymeric layer on substrate 102, template 110 is separated from the polymeric layer. FIG. 9C depicts a cross-sectional view of nanoimprint lithography stack 902 having homogeneous composite polymeric layer 904.

FIG. 10A depicts a cross-sectional view of initial contact of template 110 with composite coating 604 on substrate 102. Inhomogeneous composite coating 1000 includes regions 606 and 608. As depicted, little or no intermixing has occurred between the imprint resist in region 606 and the pretreatment composition in region 608. In FIG. 10B, template 110 has been advanced toward substrate 102 such that composite coating 1000 fills recesses of template 110. After polymerization of composite coating 1000 to yield an inhomogeneous polymeric layer on substrate 102, template 110 is separated from the polymeric layer. FIG. 10C depicts a cross-sectional view of nanoimprint lithography stack 1002 having inhomogeneous polymeric layer 1004 with regions 1006 and 1008 corresponding to regions 606 and 608 of inhomogeneous composite coating 1000. Thus, the chemical composition of composite polymeric layer 1002 is inhomogeneous or non-uniform, and includes regions 1006 having a composition derived from a mixture enriched with the imprint resist and regions 1008 having a composition derived from a mixture enriched with the pretreatment composition. The relative size (e.g., exposed surface area, surface area of template covered, or volume) of regions 1006 and 1008 may vary based at least in part on the extent of prespreading before contact of the composite coating with the template or spreading due to contact with the template. In some cases, regions 1006 may be separated or bounded by regions 1008, such that composite polymeric layer includes a plurality of center regions separated by boundaries, with the chemical composition of the composite polymeric layer 1004 at the boundaries differing from the chemical composition of the composite polymeric layer at the interior of the center regions.

Examples

In the Examples below, the reported interfacial surface energy at the interface between the imprint resist and air was measured by the maximum bubble pressure method. The measurements were made using a BP2 bubble pressure tensiometer manufactured by Krüss GmbH of Hamburg, Germany. In the maximum bubble pressure method, the maximum internal pressure of a gas bubble which is formed in a liquid by means of a capillary is measured. With a capillary of known diameter, the surface tension can be calculated from the Young-Laplace equation. For the some of the pretreatment compositions, the manufacturer's reported values for the interfacial surface energy at the interface between the pretreatment composition and air are provided.

The viscosities were measured using a Brookfield DV-II+ Pro with a small sample adapter using a temperature-controlled bath set at 23° C. Reported viscosity values are the average of five measurements.

Adhesion layers were prepared on substrates formed by curing an adhesive composition made by combining about 77 g ISORAD 501, about 22 g CYMEL 303ULF, and about 1 g TAG 2678, introducing this mixture into approximately 1900 grams of PM Acetate. The adhesive composition was spun onto a substrate (e.g., a silicon wafer) at a rotational velocity between 500 and 4,000 revolutions per minute so as to provide a substantially smooth, if not planar layer with uniform thickness. The spun-on composition was exposed to thermal actinic energy of 160° C. for approximately two minutes. The resulting adhesion layers were about 3 nm to about 4 nm thick.

In Comparative Example 1 and Examples 1-3, an imprint resist with a surface tension of 33 mN/m at an air/imprint resist interface was used to demonstrate spreading of the imprint resist on various surfaces. The imprint resist was a polymerizable composition including about 45 wt % monofunctional acrylate (e.g., isobornyl acrylate and benzyl acrylate), about 48 wt % difunctional acrylate (e.g., neopentyl glycol diacrylate), about 5 wt % photoinitiator (e.g., TPO and 4265), and about 3 wt % surfactant (e.g., a mixture of X—R—(OCH₂CH₂)_(n)OH, where R=alkyl, aryl, or poly(propylene glycol), X═H or —(OCH₂CH₂)_(n)OH, and n is an integer (e.g., 2 to 20, 5 to 15, or 10-12) (e.g., X═—(OCH₂CH₂)_(n)OH, R=poly(propylene glycol), and n=10-12) and a fluorosurfactant, where X=perfluorinated alkyl.

In Comparative Example 1, the imprint resist was disposed directly on the adhesion layer of a nanoimprint lithography substrate. FIG. 11 is an image of drops 1100 of the imprint resist on the adhesion layer 1102 of a substrate 1.7 sec after dispensation of the drops in a lattice pattern was initiated. As seen in the image, drops 1100 have spread outward from the target areas on the substrate. However, spreading beyond the target area was limited, and the area of the exposed adhesion layer 1102 exceeded that of drops 1100. Rings visible in this and other images, such as ring 1104, are Newton interference rings, which indicate a difference in thickness in various regions of the drop. Resist drop size was approximately 2.5 pL. FIG. 11 has a 2×7 (pitch)² interleaved lattice of drops (e.g., 2 units in the horizontal direction, with 3.5 units between the lines). Each following line shifted 1 unit in the horizontal direction.

In Examples 1-3, pretreatment compositions A-C, respectively, were disposed on a nanoimprint lithography substrate to form a pretreatment coating. Drops of the imprint resist were disposed on the pretreatment coatings. FIGS. 12-14 show images of the composite coating after dispensation of drops of the imprint resist was initiated. Although intermixing occurs between the pretreatment composition and imprint resist in these examples, for simplicity, the drops of imprint resist and pretreatment coating are described below without reference to intermixing. The pretreatment composition was disposed on a wafer substrate via spin-on coating. More particularly, the pretreatment composition was dissolved in PGMEA (0.3 wt % pretreatment composition/99.7 wt % PGMEA) and spun onto the wafer substrate. Upon evaporation of the solvent, the typical thickness of the resultant pretreatment coating on the substrate was in the range from 5 nm to 10 nm (e.g., 8 nm). Resist drop size was approximately 2.5 pL in FIGS. 12-14. FIGS. 12 and 14 have a 2×7 (pitch)² interleaved lattice of drops (e.g., 2 units in the horizontal direction, with 3.5 units between the lines). Each following line shifted 1 unit in the horizontal direction. FIG. 13 shows a 2×6 (pitch)² interleaved lattice of drops. The pitch value was 84.5 μm. The ratios of the volumes of resist to the pretreatment layer were in the range of 1 to 15 (e.g., 6-7).

Table 1 lists the surface tension (air/liquid interface) for the pretreatment compositions A-C and the imprint resist used in Examples 1-3.

TABLE 1 Surface Tension for Pretreatment Compositions Pretreatment Imprint resist Difference in Exam- Pretreatment surface tension surface tension surface tension ple composition (mN/m) (mN/m) (mN/m) 1 A (Sartomer 34 33 1 492) 2 B (Sartomer 36.4 33 3.1 351HP) 3 C (Sartomer 39.9 33 6.9 399LV)

In Example 1, drops of the imprint resist were disposed on a substrate having a coating of pretreatment composition A (Sartomer 492 or “SR492”). SR492, available from Sartomer, Inc. (Pennsylvania, US), is propoxylated (3) trimethylolpropane triacrylate (a multifunctional acrylate). FIG. 12 shows an image of drops 1200 of the imprint resist on pretreatment coating 1202 and the resulting composite coating 1204 1.7 seconds after dispensation of the discrete portions in an interleaved lattice pattern was initiated. In this example, the drop retains its spherical cap-like shape and the spreading of the imprint resist is limited. As seen in FIG. 12, while spreading of the drops 1200 exceeds that of the imprint resist on the adhesion layer in Comparative Example 1, the drops remain separated by pretreatment coating 1202, which forms boundaries 1206 around the drops. Certain components of the imprint resist spread beyond the drop centers, forming regions 1208 surrounding drops 1200. Regions 1208 are separated by pretreatment coating 1202. The limited spreading is attributed at least in part to the small difference in surface tension (1 mN/m) between pretreatment composition A and the imprint resist, such that there is no significant energy advantage for spreading of the drops. Other factors, such as friction, are also understood to influence the extent of spreading.

In Example 2, drops of the imprint resist were disposed on a substrate having a coating of pretreatment composition B (Sartomer 351HP or “SR351HP”). SR351HP, available from Sartomer, Inc. (Pennsylvania, US), is trimethylolpropane triacrylate (a multifunctional acrylate). FIG. 13 shows images of drops 1300 of the imprint resist on pretreatment coating 1302 and the resulting composite coating 1304 1.7 sec after dispensation of the drops in a square lattice pattern was initiated. After 1.7 sec, drops 1300 cover the majority of the surface area of the substrate, and are separated by pretreatment coating 1302, which forms boundaries 1306 around the drops. Drops 1300 are more uniform than drops 1200 of Example 1, and thus significant improvement is observed over the spreading in Example 1. The greater extent of spreading is attributed at least in part to the greater difference in surface tension (3.1 mN/m) between pretreatment composition B and the imprint resist than pretreatment A and the imprint resist of Example 1.

In Example 3, drops of the imprint resist were disposed on a substrate having a coating of pretreatment composition C (Sartomer 399LV or “SR399LV”). SR399LV, available from Sartomer, Inc. (Pennsylvania, US), is dipentaerythritol pentaacrylate (a multifunctional acrylate). FIG. 14 shows an image of drops 1400 of the imprint resist on pretreatment coating 1402 and the resulting composite coating 1404 1.7 sec after dispensation of the drops in a triangular lattice pattern was initiated. As seen in FIG. 14, drops 1400 are separated at boundaries 1406 by pretreatment coating 1402. However, most of the imprint resist is accumulated at the drop boundaries, such that most of the polymerizable material is at the drop boundaries, and the drop centers are substantially empty. The extent of spreading is attributed at least in part to the large difference in surface tension (6.9 mN/m) between pretreatment composition C and the imprint resist.

Defect density was measured as a function of prespreading time for the imprint resist of Examples 1-3 and pretreatment composition B of Example 2. FIG. 15 shows defect density (voids) due to non-filling of the template. Plot 1500 shows defect density (number of defects per cm²) as a function of spread time (sec) for 28 nm line/space pattern regions, with the defect density approaching 0.1/cm² at 0.9 sec. Plot 1502 shows defect density (number of defects per cm²) as a function of spread time (sec) over the whole field having a range of feature sizes with the defect density approaching 0.1/cm² at 1 sec. By way of comparison, with no pretreatment, a defect density approaching 0.1/cm² is typically achieved for the whole field at a spread time between 2.5 sec and 3.0 sec.

Properties of pretreatment compositions PC1-PC9 are shown in Table 2. A key for PC1-PC9 is shown below. Viscosities were measured as described herein at a temperature of 23° C. To calculate the diameter ratio (Diam. Ratio) at 500 ms as shown in Table 2, drops of imprint resist (drop size ˜25 pL) were allowed to spread on a substrate coated with a pretreatment composition (thickness of about 8 nm to 10 nm) on top of an adhesion layer, and the drop diameter was recorded at an elapsed time of 500 ms. The drop diameter with each pretreatment composition was divided by the drop diameter of the imprint resist on an adhesion layer with no pretreatment composition at 500 ms. As shown in Table 2, the drop diameter of the imprint resist on PC1 at 500 ms was 60% more than the drop diameter of imprint resist on an adhesion layer with no pretreatment coating. FIG. 16 shows drop diameter (μm) as a function of time (ms) for pretreatment compositions PC1-PC9. Relative etch resistance is the Ohnishi parameter of each pretreatment composition divided by the Ohnishi parameter of the imprint resist. Relative etch resistance of PC1-PC9 (the ratio of etch resistance of the pretreatment composition to the etch resistance of the imprint resist) is shown in Table 2.

TABLE 2 Properties of Pretreatment Compositions PC1-PC9 Surface Viscosity Diam. Rel. Etch Pretreatment Tension (cP) Ratio Resistance Composition (mN/m) at 23° C. at 500 ms (Ohnishi Ratio) PC1 36.4 ± 0.1 111 ± 1  1.59 1.3 PC2 37.7 ± 0.1 66.6 ± 0.3 1.86 1.5 PC3 33.9 ± 0.1 15.5 ± 0.1 2.46 1.1 PC4 41.8 ± 0.1 64.9 ± 0.3 1.92 1.9 PC5 38.5 ± 0.3 18.4 ± 0.1 2.73 1.7 PC6 NA NA 1.75 0.9 PC7 35.5 ± 0.3  8.7 ± 0.1 2.36 1.1 PC8 39.3 ± 0.1 10.0 ± 0.1 2.69 0.9 PC9 38.6 ± 0.1 143 ± 1  1.95 0.9 Imprint 33 1.00 1.0 Resist PC1: trimethylolpropane triacrylate (Sartomer) PC2: trimethylolpropane ethoxylate triacrylate, n ~1.3 (Osaka Organic) PC3: 1,12-dodecanediol diacrylate PC4: poly(ethylene glycol) diacrylate, Mn, avg = 575 (Sigma-Aldrich) PC5: tetraethylene glycol diacrylate (Sartomer) PC6: 1,3-adamantanediol diacrylate PC7: nonanediol diacrylate PC8: m-xylylene diacrylate PC9: tricyclodecane dimethanol diacrylate (Sartomer)

Pretreatment compositions PC3 and PC9 were combined in various weight ratios to yield pretreatment compositions PC10-PC13 having the weight ratios shown in Table 3. Comparison of properties of PC3 and PC9 with mixtures formed therefrom revealed synergistic effects. For example, PC3 has relatively low viscosity and allows for relatively fast template filling, but has relatively poor etch resistance. In contrast, PC9 has relatively good etch resistance and film stability (low evaporative loss), but is relatively viscous and demonstrates relatively slow template filling. Combinations of PC3 and PC9, however, resulted in pretreatment compositions with a combination of advantageous properties, including relatively low viscosity, relatively fast template filling, and relatively good etch resistance. For example, a pretreatment composition having 30 wt % PC3 and 70 wt % PC9 was found to have a surface tension of 37.2 mN/m, a diameter ratio of 1.61, and an Ohnishi parameter of 3.5.

TABLE 3 Composition of Pretreatment Compositions PC10-PC13 Pretreatment PC3 PC9 Composition (wt %) (wt %) PC10 25 75 PC11 35 65 PC12 50 50 PC13 75 25

FIG. 17A shows a plot of viscosity for pretreatment compositions including various ratios of PC3 and PC9 (i.e., from 100 wt % PC3 to 100 wt % PC9). FIG. 17B shows drop diameter (measured as described with respect to Table 2) for PC3, PC13, PC12, PC11, PC10, and PC9. FIG. 17C shows surface tension (mN/m) versus fraction of PC3 and PC9.

FIG. 18 shows ratios of the etch rate of pretreatment composition to the etch rate of the imprint resist for PC3, PC9, mixtures of PC3 and PC9, and the imprint resist referenced in Table 2. Thin cured films of the pretreatment compositions PC9 (1800); 25 wt % PC3+75 wt % PC9 (1802); 30 wt % PC3+70 wt % PC9 (1804); PC12 (1806); PC3 (1808)) were prepared on silicon substrates. Thin cured films of the same thickness of the imprint resist were also prepared. The samples were etched in a plasma etcher with fluorocarbon etch chemistry. The etch processes were performed using a reactive ion etch tool from Trion Technology with 75 W RIE power and 150 W ICP power, 5 sccm CF₄ and 30 sccm argon at 120 mTorr, and a process time of 90 s. The thickness of each thin film sample before and after etching was measured by reflectometry.

PC3 (1,12-dodecanediol diacrylate) and PC9 (tricyclodecane dimethanol diacrylate) are both difunctional acrylates. PC9 has a cyclic hydrocarbon backbone which was expected to provide relatively high etch resistance. Based on the Ohnishi number, PC9 was expected to have a higher etch resistance (lower etch rate) than the imprint resist, and PC3 was expected to have a lower etch resistance (higher etch rate) than the imprint resist. The results shown in FIG. 18 indicate that PC3 actually has a similar, though slightly higher, etch resistance (lower etch rate) than the imprint resist. PC9 has an even higher etch resistance (lower etch rate) than the imprint resist, with an etch rate of about 70% that of the imprint resist. The higher etch resistance of PC3 and PC9 than predicted based on the Ohnishi numbers may be related, at least in part, to the greater degree of crosslinking in PC3 and PC9 relative to the imprint resist.

In another example, PC1 was used in a standard imprint process with the imprint resist referenced in Table 2. The spread time was short enough to ensure that PC1 and the imprint resist did not have time to completely mix, so there was a non-uniform distribution of PC1 and the imprint resist across the imprint field, with PC1 concentrated at drop boundary regions. Atomic force microscope (AFM) measurements were made of imprint feature heights before and after etching with oxygen etch chemistry to determine if any difference in etch rate between drop center and drop boundary regions could be detected. The oxygen etches were performed using a reactive ion etch tool from Trion Technology at 70 W with 5 sccm oxygen and 20 sccm argon at 15 mTorr and a process time of 20 s. Plot 1900 in FIG. 19A shows imprint feature height (nm) measured at 5 μm intervals along a 160 μm horizontal distance on the imprint field. It can be difficult to determine the location of drop centers and drop boundaries visually, so measurements were made across a distance equal to the drop pitch so that at least one drop boundary would be included in the set of measurements. The drop pitch in these samples was ˜158 μm in the horizontal direction. Plot 1900 shows a pre-etch average feature height of about 58.1 nm with a range of about ±1.5 nm. Plot 1910 in FIG. 19B shows post-etch imprint feature height measured at 5 μm intervals along a 320 μm horizontal distance on the imprint field. The post-etch average feature height was about 46.4 nm with a range of about ±1.5 nm. Therefore, no significant difference in etch rate was observed along this scan length, which would cover at least two drop boundary regions, indicating a close match of etch rate between the two materials under typical imprint conditions. Based on the Ohnishi number, PC1 is expected to have an etch rate approximately 30% greater than that of the resist. However, since PC1 (trimethylolpropane triacrylate) is a trifunctional acrylate, the higher degree of crosslinking relative to the resist may have contributed to an increase of the etch resistance, such that the etch rates of PC1 and the imprint resist were found to be similar for the two materials.

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A nanoimprint lithography method comprising: disposing a pretreatment composition on a nanoimprint lithography substrate to yield a liquid pretreatment coating on the nanoimprint lithography substrate, wherein the pretreatment composition comprises a polymerizable component; disposing discrete portions of an imprint resist on the pretreatment coating, wherein the imprint resist is a polymerizable composition; forming a composite polymerizable coating on the nanoimprint lithography substrate as each discrete portion of the imprint resist spreads on the liquid pretreatment coating; contacting the composite polymerizable coating with a nanoimprint lithography template defining recesses; polymerizing the composite polymerizable coating to yield a composite polymeric layer defining a pre-etch plurality of protrusions corresponding to the recesses of the nanoimprint lithography template, wherein at least one of the pre-etch plurality of protrusions corresponds to a boundary between two of the discrete portions of the imprint resist, and the pre-etch plurality of protrusions have a variation in pre-etch height of ±10% of a pre-etch average height; separating the nanoimprint lithography template from the composite polymeric layer; and etching the pre-etch plurality of protrusions to yield a post-etch plurality of protrusions, wherein the post-etch plurality of protrusions have a variation in post-etch height of ±10% of a post-etch average height, and the pre-etch average height exceeds the post-etch average height.
 2. The nanoimprint lithography method of claim 1, wherein the pre-etch average height is up to 1 μm, up to 500 nm, or up to 200 nm.
 3. The nanoimprint lithography method of claim 1, wherein the variation in post-etch height is ±5% of the post-etch average height.
 4. The nanoimprint lithography method of claim 1, wherein at least two of the pre-etch plurality of protrusions correspond to boundaries between two of the discrete portions of the imprint resist.
 5. The nanoimprint lithography method of claim 1, wherein each protrusion in the pre-etch plurality of protrusions has a width in a range of 5 nm to 100 μm along a dimension of the nanoimprint lithography substrate.
 6. The nanoimprint lithography method of claim 1, wherein the pre-etch plurality of protrusions corresponds to a linear dimension of up to 50 mm along a dimension of the nanoimprint lithography substrate.
 7. The nanoimprint lithography method of claim 1, wherein etching the pre-etch plurality of protrusions comprises exposing the plurality of protrusions to an oxygen- or halogen-containing plasma.
 8. The nanoimprint lithography method of claim 1, wherein the boundary between the two of the discrete portions of the imprint resist is formed from an inhomogeneous mixture of the imprint resist and the pretreatment composition.
 9. The nanoimprint lithography method of claim 1, wherein the pre-etch average height exceeds the post-etch average height by at least 1 nm.
 10. The nanoimprint lithography method of claim 1, wherein the pre-etch height and the post-etch height are assessed at intervals in a range of 1 μm to 50 μm along a dimension of the nanoimprint lithography substrate.
 11. The nanoimprint lithography method of claim 1, wherein the pre-etch height and the post-etch height are assessed by atomic force microscopy, reflectometry, ellipsometry, or profilometry.
 12. The nanoimprint lithography method of claim 1, wherein the interfacial surface energy between the pretreatment composition and air exceeds the interfacial surface energy between the imprint resist and air or between at least a component of the imprint resist and air.
 13. The nanoimprint lithography method of claim 1, wherein the difference between the interfacial surface energy between the pretreatment composition and air and the interfacial surface energy between the imprint resist and air is in a range of 0.5 mN/m to 25 mN/m, 0.5 mN/m to 15 mN/m, or 0.5 mN/m to 7 mN/m; the interfacial surface energy between the imprint resist and air is in a range of 20 mN/m to 60 mN/m, 28 mN/m to 40 mN/m, or 32 mN/m to 35 mN/m; and the interfacial surface energy between the pretreatment composition and air is in a range of 30 mN/m to 45 mN/m.
 14. The nanoimprint lithography method of claim 1, wherein the viscosity of the pretreatment composition is in a range of 1 cP to 200 cP, 1 cP to 100 cP, or 1 cP to 50 cP at 23° C.; and the viscosity of the imprint resist is in a range of 1 cP to 50 cP, 1 cP to 25 cP, or 5 cP to 15 cP at 23° C.
 15. A nanoimprint lithography stack formed by the nanoimprint lithography method of claim
 1. 16. A method for manufacturing a device, the method comprising the nanoimprint lithography method of claim
 1. 17. The device formed by the method of claim
 16. 18. A nanoimprint lithography stack comprising: a nanoimprint lithography substrate; and a composite polymeric layer on the nanoimprint lithography substrate, wherein the composite polymeric layer is formed from discrete portions of an imprint resist on a pretreatment coating and defines a pre-etch plurality of protrusions, at least one of the protrusions corresponding to a boundary between two of the discrete portions of the imprint resist, the pre-etch plurality of protrusions have a variation in pre-etch height of ±10% of a pre-etch average height; wherein after etching of the pre-etch plurality of protrusions to yield a post-etch plurality of protrusions, the post-etch plurality of protrusions has a variation in post-etch height of ±10% of a post-etch average height, and the pre-etch average height exceeds the post-etch average height.
 19. The nanoimprint lithography stack of claim 18, wherein the boundary between the two of the discrete portions of the imprint resist is formed from an inhomogeneous mixture of the pretreatment composition and the imprint resist.
 20. The nanoimprint lithography stack of claim 18, wherein the variation in post-etch average height is ±5% of the post-etch average height. 